A headphone shaped, for example, as shown in FIG. 1 is conventionally in practical use. FIG. 1 is a side view of a headphone in which an arm 2 extends upward from a left housing 1 and is connected to a right housing on the opposite side not shown in the figure. A driver unit driven by an audio signal provided via a cable 4 is accommodated within the housing 1, and an ear pad 3 is provided on the outside of the housing 1.
When a headphone having the shape shown in the FIG. 1 is constructed, the housing 1 and an attachment portion of the arm 2 are integrally formed with resin, whereby the headphone including a comparatively small number of components with simple configuration is constructed.
If the housing 1 and the attachment portion of the arm 2 are integrally formed with resin, it is, however, necessary to cut part of the housing 1 away at the point where the attachment portion of the arm 2 and the housing 1 overlap when the housing 1 is formed with resin, and a concave portion 3a that corresponds to the cutaway portion of the housing 1 comes into existence when the ear pad 3 made of a relatively soft sponge-like resin or the like is attached.
The reason why this concave portion is caused will be explained. When the housing 1 and the attachment portion of the arm 2 are integrally formed with resin, a periphery of the integrally formed housing 1 is formed as, for example, shown in FIG. 19. FIG. 2A, FIG. 2B and FIG. 2C show a rear surface, side surface and front surface of the periphery of the integrally formed housing 1 respectively, and the driver unit not shown in the figure is disposed on the rear surface of that shown in FIG. 2A, and the front surface shown in FIG. 2C is exposed to the outside in the assembled state with the ear pad 3 attached.
As shown in FIGS. 2A and 2C, a flange 1a is formed on the housing 1 in approximately circular shape to attach the ear pad 3 and by covering the flange 1a with the ear pad 3, the ear pad is attached. However, in order that the housing 1 and the attachment portion of the arm 2 are integrally formed, it is impossible to provide the flange 1a at the point where the housing 1 overlaps with the attachment portion of the arm 2.
Specifically, as shown in FIG. 2B in this example, a molding die is formed with resin on the core side and on the cavity side separately based on a parting line P, and since it is intended that the attachment portion of the arm 2 is formed, it becomes impossible to form the flange 1a at the part where the attachment portion of the arm 2 is formed (namely at an undercut area). Therefore, there is no support member which supports the ear pad 3 at the position where the arm 2 is overlapped with the attachment portion, and a concave portion 3a shown in FIG. 18 comes into existence.
As the molding die, the simplest mold of two-plate structure is employed in this example, and although it is possible to form a flange at the undercut portion using a more complicated mold such as a mold of slide core, there may occur problems that production cost rises and then the price of the headphones rises if this kind of complicated mold is used to form the headphone.
Although depending on the shape of the ear pad 3 it is possible to make the concave portion 3a inconspicuous, also in this case, the corresponding part of the ear pad 3 is easily dented once it has been pressed, owing to lack of a flange. Also, the ear pad 3 is partly dented once it has been worn by a listener, owing to lack of a flange at the corresponding part, so that the listener feels discomfort at wearing it on his/her auricle. In addition, the occurrence of such concave portion 3a causes the ear pad 3 to detach from the housing 1 easily. Making matters worse, there has been a problem in which, once the ear pad 3 has changed and deteriorated over time, the earpad 3 tends to tear easily from the concave portion.
Also, as another problem, it is necessary to pass a cable for supplying an audio signal or the like from the outside to the driver unit accommodated in the housing of this kind of headphone. Note that it has been necessary to provide a mechanism that helps the cable lock midway along the housing so that, when the cable attached to the headphone is being pulled from the outside with some force, the cable will not detach from the driver unit by the force directly affecting the portion where the driver unit and the cable are connected.
Specifically, as shown, for example, in FIG. 3 there is provided the housing 8 in which a driver unit that outputs an audio signal is accommodated within the inside 8a thereof. Then, a through-hole 8b is provided on the side surface of the housing 8 formed with resin, and a cord 9 is then passed through the through-hole 8b. One end of the cord 9 passed through this through-hole 8b is soldered and connected to the driver unit within the housing 8. Further, in this example, a knot 9a made by tying the cord 9 once is formed within the housing 8 so that the portion where the cord 9 and the driver have been soldered together does not separate if the cord 9 is pulled from the outside, in which the knot 9a serves as a stopper as being stopped by the through-hole 8b and prevents the soldered portion and the like from being affected by a force when the cord 9 is being pulled from the outside.
Although this construction can prevent the cord from being disconnected, it is necessary to pass the cord 9 through the through-hole 8b of the housing 8 and to form the knot 9a on the cord itself when the headphone is being assembled so that there has been a problem in which the assembly process is extremely time-consuming.